Fresh water is rarer than you might think. In fact, it's only 3% of the planet's supply with around 75% stored in glaciers.

So we should cherish every drop, and pay attention to ways in which we can cut down in all areas, not just agriculture.

Feeding the world, however, is a job which isn't going to disappear any time soon. So how can we do it with less water?

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Dry farming

Today, there are urban farms without soil, where plant roots are misted rather than irrigated, with a water saving of 95%. The UN estimates that we'll nearly 10 billion people -- the majority living in urban areas -- to feed by 2050, we are increasingly looking to tech to solve our problems.

But sometimes the answer is as old as the hills where the food is grown.

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Dry farming is a method which uses no irrigation. Plants are encouraged to dig their roots deep, and draw on natural water reserves in the soil. The ground is prepared to lock in as much natural moisture as possible. Farming this way is optimum in certain terrain where groundwater naturally accumulates, such as at the base of a mountain.

There's evidence to suggest the Incas farmed in similar conditions in South America. Much of Europe's lucrative wine industry is dry farmed. And today winemakers in drought-stricken California are following suit.

"In France irrigation is forbidden -- you cannot irrigate grape vines," says Tod Mostero, viticulturist at Dominus Estate in California's Napa Valley. "There's a reason for that. It makes sense that you plant crops where they belong, and not in places where they don't."

Dominus have dry farmed for years, and the water saving is enormous. By not watering their 100,000 vines, one million gallons of water is saved each month.

"Frankly I consider irrigation of vineyards a pure waste of water," says Mostero.

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In California, where 80% of water is given over to agriculture, such savings are not to be dismissed. And given the increasing pressure on growers of water-thirsty crops such as almonds, dry farming could be an option for more farmers. Potatoes, tomatoes and quinoa are already grown this way locally.

Root of the problem

For the winemakers, taste is, of course, key. Happily for Mostero, Dominus grapes are more mouth-watering than their irrigated counterparts.

"We don't believe you can make a wine that has true character, or at least the character of your vineyard, unless it's dry farmed. Because only if it's dry farmed will it have that connection with the soil."

Thanks to location requirements, dry farming is not for everyone. Another downside is that yields can be lower. There is another water-saving technique farmers can call on which has neither of these restrictions: partial root drying.

Pioneered by University of Lancaster professor and crop scientist Bill Davies, it involves splitting a plant's root system in two, watering one half, and starving the other. The process is then reversed, and uses roughly half the water of traditional irrigation.

Partial root drying has been successfully trialled on a number of crops, including water-hungry rice. "Rice uses a ridiculous amount of water," says Davies. "Probably about a third of fresh water on the planet. We have to grow rice with less water." Allowing a paddy to dry out before replenishing can drastically cut water usage.

"We have advised Chinese farmers, if you jump in the paddy and you land and you can see your footprints, don't irrigate," says Davies.

"Farmers throw water around. Most irrigation systems are pretty imprecise. But as the climate changes it's getting hotter and drier in many food-growing areas. Our systems have to change. Farming has to respond now."